This invention relates to semiconductor chip packaging and, particularly, to leadframe packages having two or more semiconductor die attached to a leadframe.
A conventional leadframe consists of a generally planar metal piece, having peripheral leads arranged about a centrally situated die paddle. In a conventional leadframe package, a die is affixed to the die paddle by attaching the back side of the die to the die paddle using an adhesive, and electrically connecting the die to the leads by wire bonding between wire bond pads on the die and wire bond sites on the leads. It is known to construct a leadframe package having two or more semiconductor die attached to a leadframe and interconnected by wire bonding.
For example, U.S. Pat. No. 6,265,763 describes various multi chip package configurations having a first (lower) die affixed to a leadframe die paddle, and a second (upper) die stacked upon the first die, both die being interconnected to the leadframe by wire bonding. In some configurations the first die has peripheral wire bond pads and the second die has a smaller footprint than the first, and the second die is accordingly stacked directly onto the upper (active) side of the first die. In other configurations the first die has peripheral wire bond pads and the footprint of the second die is too large to fit on the active side of the first die without interfering with the wire bond pads on the first die; in such configurations a spacer having a suitably small footprint is onto the active side of the first die, and the second die is affixed over the first die.
As U.S. Pat. No. 6,285,763 points out, stacking wire bonded die in such a fashion can be effective for die having peripheral wire bond pads, but is unsuitable for die having the bond pads situated near a center line of the die. U.S. Pat. No. 6,285,763 proposes a multi chip package having at least one peripheral pad die and at least one central pad die, in which the leadframe has a central die paddle and leads separated from the die paddle by a gap. A peripheral pad die is attached in a conventional fashion onto the die paddle on one side (the “top” side) of the leadframe, and a central pad die is attached partly on the die paddle and partly on the leads on the other side (the “bottom” side) of the leadframe, with the active side of the die toward the leadframe and the central pads situated in the part of the die spanning the gap. The conventionally attached top die is interconnected directly to the central pad bottom die by wire bonds running between peripheral bond pads on the top die and central bond pads on the bottom die; and both the conventionally attached top die and the bottom die are wire bonded to the leads. The completed wire bonded assembly is then encapsulated to enclose and protect all the die and the wire bonds.
The extent to which a wire bonded package can be made thin is limited by the fact that the encapsulant must fully cover the wire bond loops over the die. That is, the wire bond loop height imposes a thickness dimension (loop height plus encapsulant thickness over the loops) in addition to the thickness of the leadframe and the thickness of the die. In a drive toward thinner packages, efforts have been made to reduce the wire bond loop height.